A conventional keyboard such as an alpha numeric keyboard of the type having membrane or other type switch for each key position, has a switch actuator at each key position which comprises, in general, a fixed frame, a plunger slideably mounted in the frame, and a key top secured to the upper or force-receiving end of the plunger. When the key top is pressed, the plunger is moved downwardly and effects closure of the switch. Keyboard switches for alpha numeric keyboards are constructed and designed such that their dimensions will conform to industry accepted standards so that all keyboards will be similar to each other to the extent that the operators will be able to use keyboards from different manufacturers.
The older keyboards were usually provided with switch actuators that have a somewhat greater overall height than is permitted by the standards that are being followed at present and which will apply to many keyboards manufactured in the future. The newer standards, commonly referred to as DIN Standards, specify the dimensions, the slope of the keyboard, and the stroke required for the key positions in a manner such that many presently available keyboards cannot be brought into conformity with the standards. When designing a keyboard which will satisfy the DIN standards, it is desirable to have switch actuators of a reduced overall height, as compared with previously known actuators and which have a relatively long stroke, notwithstanding the reduced overall height of the actuator. The present invention in accordance with one aspect thereof, is directed to the achievement of an actuator which will meet these requirements of a long stroke coupled with reduced height.
The invention is further directed to the achievement of an actuator comprising a frame, a plunger, and a key top with the plunger being capable of assembly to the frame and to the key top in any one of several angular orientations. This feature is advantageous in certain types of actuators that are designed to provide for different operating modes with standard parts, as explained for example, in U.S. application Ser. No. 354,318, now U.S. Pat. No. 4,417,115 filed on the same date as this application.
A low profile switch actuating assembly in accordance with the invention comprises a frame having a fixed end and a free end and having an axial opening extending into the free end towards the fixed end. A plunger is slideably mounted in the opening, the plunger having a lower end which is proximate to the fixed end of the frame and a force-receiving end which is proximate to the free end of the frame. The plunger is slideably movable from a normal position to a depressed position, the force-receiving end of the plunger being located beyond the free end of the frame when the plunger is in the normal position and being movable towards the free end when the plunger is moved to the depressed position. The force-receiving end of the plunger has a key top thereon which is pressed to move the plunger to the depressed position. A switch actuating assembly in accordance with the invention is particularly characterized in that the key top has an underside which is opposed to the free end of the frame and a frame-receiving recess is provided in the underside, the recess being dimensioned to receive the free end of the frame upon movement of the key top towards the frame. The force-receiving end of the plunger has a plurality of radially extending arms integral therewith, the arms being in the plane which extends normally of the axis of the plunger. The force-receiving end of the plunger is received in the underside of the key top with adjacent portions of the arms, which are adjacent to the axis of the plunger, being in the force-receiving recess and with outer end portions of the arms being received in arm-receiving recesses. The arm-receiving recesses extend from the sidewalls of the frame-receiving recess. The free end of the frame has arm-receiving slots therein extending radially from the axial opening, the arm-receiving slots being dimensioned to receive the adjacent portions of the plunger arms whereby upon movement of the plunger from the normal position to the depressed position, the free end of the frame is received in the frame-receiving recess and the adjacent portions of the plunger arms enter the arm-receiving slots.
In accordance with a further embodiment, an actuator in accordance with the invention is characterized in that the plunger arms extend from the plunger at equally spaced angular intervals and the arm-receiving recesses and the arm-receiving slots extend at the same angular intervals as the plunger arms. The plunger is capable of assembly to the frame in at least two different angular orientations. In accordance with a further embodiment, the plunger has four plunger arms which are secured in the arm-receiving recesses of the key top and the switch actuating assembly is mounted on a membrane switch which is closed when the plunger is moved to its depressed position.